Question

1. Explain how WUSHEL and CLAVATA establish a feedback loop to control shoot apical meristem size (2 pts)
   
   
   
   
2. In addition to water and oxygen, seeds commonly need a secondary environmental signal to germinate, other than exposure to light, briefly describe two other environmental signals that can promote germination (2pts)
   
   
   

Answer 1

Ans) WUSHEL-CLAVATA feedback loop is important in controlling meristem size of shoot apical where the pluripotent stem cells responsible for maintaining shoot meristems are controlled by CLAVATA-WUSCHEL. This pathway co-ordinates the proliferation of the stem cell along with its differentiation and hence helps in the signaling pathway allowing feedback signaling. The CLAVATA-WUSHCEL pathway is a central regulatory pathway which helps in proliferation and differentiation. WUS is a transcription factor and CLV3 is a peptide that helps with differentiation.

WUS is a transcription factor which initiates the expression of the shoot meristem from the pluripotent stem cells. This is activated majorly with help of cytokinin signaling. Once the stem cell become meristem cell of shoot or it is differentiated, the differentiated shoot meristem cell in proliferated in presence of CLV3(CLAVATA) and increases its concentratioh. When the concentration increases a lot, the CLV3 triggers feedback signaling that stops WUS from further expressing the pluripotent stem cells into differentiated shoot meristem cells.

Ans) Two environment factor that is important for germination of the seeds are:-

1. Temperature – The temperature can impact the rate of seed germination where some seeds require moderate temperature to grow while some require cold. Some seeds also need alternate phases for growth. The rate of seed deterioration mainly is controlled by moisture and temperature.
2. pH – The pH impacts the seed germination where in most cases it is observed that high pH negatively impacts the germination of seed.